JIN, et al [3–5], studied the effects of structural parameters

of pneumatic components on condensation according to a large number of experimental data。 Integrated with  fluid net theory, physical characteristics used for analyzing the system condensation were presented; the distribution of experimental data revealing when internal, external or no condensation would occur。 The state and movement parameters of the compressed air during the exhausting process of pneumatic systems were derived by using mathematical analysis; Effect of different factors on condensation in pneumatic system was investigated by using dimensional analysis。 The above work provided a novel approach for the quantitative analysis of condensation。

ZHANG[6] studied the internal condensation from the perspective of  phase  change。  The  effects of heat  transfer

JIN Yingzi, et al: Comprehensive Parameter for Analyzing Condensation in Pneumatic System

coefficient, condensation coefficients and boundary conditions on the formation and growth of water droplets in compressed air were studied via numerical simulation methods。

IKEO,  et  al[7–8],  simulated  the  filling  and discharging

process of pneumatic systems by using bond graph simulation program(BGSP), discussed the effects of condensation coefficients and boundary conditions on condensation, and proposed condensation critical curves under different condensation coefficients, which provided a theoretical basis for the quantitative analysis of condensation within a certain range of physical parameters。 LI, et al[9], provided a numerical method to determine the internal condensation。 The flow computation for discharging  process  of  pneumatic  system  was  simulated

and the water droplet production calculated。

Amongst the factors, the effect of structural  parameters of the system components is obvious。 However, the effect can not be entirely determined quantitatively by theoretical methods。 The research on the influence of a single factor depends mostly on experimental data。 Currently, most studies focus on the influence of single factors on condensation, and the methods of preventing condensation are proposed from the point of such single factors。 If the condensation could be discriminated or prevented based upon comprehensive system parameters, it would  have great significance for predicting condensation at the design stage or before the system was utilized。

In this paper, the comprehensive parameters  composed of different single factors were proposed based on a large amount of experimental data combined with theoretical analysis of state and motion parameters of compressed air。 Then, the method to distinguish between the internal and external condensation by quantitative parameters was proposed。 This work provides a method for experimental study and analysis of pneumatic system condensation。

2 Experimental Setup and Principles

As shown in Fig。 1, the experimental setup consists of a compressed air source, relief valve, directional valve, large vessel, cylinder (experimental container), timer, and a certain length of pipe。 The large vessel is used to provide gas。 The internal temperature and pressure of larger vessel are measured by a temperature sensor and a pressure sensor, respectively。 The average temperature and humidity are recorder by hygrothermograph。 The charging process and discharge process of cylinder (experimental container) can be implemented by reversing valve。 The reversing valve is controlled by timer。 The formation of the water droplet or ice was observed after eight hours of continuous operation of cylinder (container)。